why does sh.exe swallow `\` and how to escape `\`? - windows

Question

sh -c 'ls C:\Users\timothee'
gives:
ls: cannot access 'C:Userstimothee': No such file or directory
sh -c 'ls C:\\Users\\timothee'
gives:
ls: cannot access 'C:Userstimothee': No such file or directory
these work:
sh -c 'ls C:\\\Users\\\timothee'
sh -c 'ls C:/Users/timothee'
but isn't there a better way?
I'm trying to programmatically call a shell (bash or sh) command using CreateProcess and escape it properly, but the weird swallowing of backslash makes this awkward. See C example below:
is this the best way below, using 6(!) backward slashes?
(my full program would have to convert an input eg echo C:\\Users\\timothee to this:
echo C:\\\\\\Users\\\\\\timothee)
#ifdef _WIN32
#include <windows.h>
#include <stdio.h>
#include <tchar.h>
#include <cstdlib>
#include <string>
#include <algorithm>
#include <stdio.h>
#include <windows.h>
#include <stdio.h>
#include <tchar.h>
void _tmain2(TCHAR *argv)
{
// adapted from https://stackoverflow.com/questions/42531/how-do-i-call-createprocess-in-c-to-launch-a-windows-executable
STARTUPINFO si;
PROCESS_INFORMATION pi;
ZeroMemory( &si, sizeof(si) );
si.cb = sizeof(si);
ZeroMemory( &pi, sizeof(pi) );
// Start the child process.
if( !CreateProcess( NULL, // No module name (use command line)
argv, // Command line
NULL, // Process handle not inheritable
NULL, // Thread handle not inheritable
FALSE, // Set handle inheritance to FALSE
0, // No creation flags
NULL, // Use parent's environment block
NULL, // Use parent's starting directory
&si, // Pointer to STARTUPINFO structure
&pi ) // Pointer to PROCESS_INFORMATION structure
)
{
printf( "CreateProcess failed (%d).\n", GetLastError() );
return;
}
// Wait until child process exits.
WaitForSingleObject( pi.hProcess, INFINITE );
// Close process and thread handles.
CloseHandle( pi.hProcess );
CloseHandle( pi.hThread );
}
int main (int argc, char *argv[]) {
//char s[] = "echo ok1 && echo ok2"; // bad (prints: ok1 && echo ok2)
//char s[] = "sh -c 'echo ok1 && echo ok2'"; // ok: prints ok1\nok2
//char s[] = "sh -c 'echo C:\\Users\\timothee\\'"; // error
//char s[] = "sh -c 'echo C:/Users/timothee'"; // ok but I want \, not / as some windows program don't understand /
//char s[] = "sh -c 'echo C:\\\\Users\\\\timothee'"; // BUG: prints: C:Userstimothee
char s[] = "sh -c 'echo C:\\\\\\Users\\\\\\timothee'"; // prints: C:\Users\timothee
_tmain2(s);
return 0;
}
#endif //win32
links:
https://github.com/vim/vim/issues/371
https://github.com/boot2docker/boot2docker-cli/issues/301

Answer 1

The problem is that the back-slash needs to be escaped twice:
First by the shell where you invoke the sh command
Then a second time by the sh command itself.
So when you use the command-line
sh -c 'ls C:\\\Users\\\timothee'
the running shell will remove one back-slash and pass 'ls C:\\Users\\timothee to the sh command.
The sh command in turn needs that double back-slash in its own processing, and will pass C:\Users\timothee to the ls command.